All you have to do is collect 100 PartyPoints within 90 days and the $50 and your winnings are all yours (you can withdraw this money). If you fail to collect the 100 PartyPoints in the allotted time, you will lose the $50 bonus (or whatever remains from it), but you can withdraw what you have won.

I hope this helps you. If you have further questions, please do not hesitate to ask.